Quantum particles can tunnel through long-range barriers, Austrian research reveals

Quantum tunneling is a puzzling process -- particles including atoms, under the right conditions, can tunnel right through barriers that should be impenetrable.

In our everyday world, a pendulum of a grandfather clock will stay at rest until the clock is wound, adding energy to the system. On the subatomic scale, energy levels are uncertain until they are measured. If our everyday world worked that way, the pendulum of an unwound grandfather clock could be seen resting in any position.

This process is the guiding principle behind transistors, which are essential for electronic components, even today. This tunneling process in electronics, until now, involved a single particle tunneling through a solitary barrier.

Austrian researchers have found a way for particles to pass through up to five of these barriers at one time.

Hanns-Christoph Nägerl, a member of the Institute for Experimental Physics at the University of Innsbruck in Austria, led a team of researchers experimenting with quantum tunneling.

Cesium atoms were brought down to nearly 460 degrees below zero Fahrenheit, near absolute zero. They were placed in a container, in a criss-cross pattern called a lattice. This was then excited by powerful lasers, creating bright mountains and dark valleys of energy, running along ribbons. The low-energy regions acted as barriers to atoms, creating a situation similar to marbles on a washboard. At these low temperatures, movement of atoms was nearly nonexistent, leaving quantum tunneling as the only means of travel.

Investigators applied a charge to the experiment, which would push the atoms toward the barriers. This is like tilting the washboard to one side, causing the marbles to drop down levels. They found that quantum particles assisted each other in tunneling through the low-energy regions, under conditions where a single particle could not accomplish the task. The team found that particles could shift positions, even if other particles blocked their path.

"Very similar to a massive object moving in the Earth's gravitational field, the tunneling atoms should loose potential energy when they move down the washboard," researchers stated in a press release announcing their findings.

The quantum tunneling effect allows radioactive atoms to decay, and is essential to fusion reactions in stars.

Future applications of this research could include advances in quantum computers, or in medicine. Just as transistors led to integrated circuit boards and computer chips, changing the world forever, this new discovery could herald a new age in information processing.

Investigation of the quantum tunneling behavior of ultra-cold cesium atoms was profiled in the journal Science.